Seems like this was done for the 2017 Air Self-Defense Force Kumagaya Base Sakura Festival. The starfighter in question was serial number: 683B-3204 located at Kumagaya Airbase - JASDF Kumagaya Airbase
For those that do not know:
Brave Witches is a Japanese anime series that is a spin-off of the popular Strike Witches franchise. The series is set in an alternate version of World War II, where humanity is under attack by an alien race called the Neuroi.
The story follows a group of young female witches, known as the 502nd Joint Fighter Wing, who are tasked with defending their homeland against the Neuroi threat. The witches possess magical powers that allow them to fly with the aid of specialized mechanical devices, called Striker Units, and fight off the Neuroi using various weapons.
Direct translation from 「ブレイブウィッチーズ」の航空自衛隊熊谷基地さくら祭での展開内容を公開！｜「ブレイブウィッチーズ」の航空自衛隊熊谷基地さくら祭での展開内容を公開！
Fighter F-104 wrapped with “Brave Witches” It was decided to decorate
the fighter F-104 displayed at Kumagaya Air Base with “Brave Witches”!
Please take a look at the fighters wrapped in unit emblems, Hikari and Shimohara!
Nearby is the T-6G, which Hikari Karibuchi used as a model for the practice striker unit in the first episode. Please stop by either!
Here is the voice actor for each of their characters showing off the character they voice on the plane